The invention relates to a friction brake for a shaft and a mounting part which can rotate in relation to one another about a rotational axis, comprising two brake elements, the first brake element of which has a first friction surface and has to be mechanically connected to the bearing, and the second brake element has a second friction surface and has to be mechanically connected to the shaft, and an activation mechanism whose force effect, which can be switched on or off, presses the two brake elements against one another during a braking process or stopping process in such a way that the two friction surfaces bear against one another and are in contact in the region of a contact surface.
Such a friction brake is known, for example, from DE 100 46 903 C2. It is an emergency stop brake or stopping brake of an electric drive. The friction surfaces of these friction brakes which act against one another are of equal size and both annular. They each form in their entirety the given contact surface during the braking/stopping process. In a mechanically excited and controlled friction brake of this type, said contact surface should, on the one hand, not be too large in order to maximize the magnetic flux density passing through here, and therefore to maximize the magnetic cohesion which can be achieved. On the other hand, in order to conduct away heat a surface which is as large as possible is desirable. The compromise which always has to be made in practice in this regard can lead, in particular in the case of strong or long braking processes, to an accumulation of heat at the friction surfaces. The resulting overheating may reduce the braking effect or stopping effect.
In other known friction brakes such as, for example in the case of disk brakes which are used in a motor vehicle, the braking behavior may be impaired as a result of excessive generation of heat at one of the friction surfaces which are involved.
In order to avoid overheating, internally ventilated brake disks are also used. Because of the poor thermal conductivity of the steel of the brake disks, this measure does not have any effect in the case of strong, brief braking.
In the case of two-wheels, perforated brake disks have been used in order to reduce the vapor pressure occurring when there is moisture on the friction surface. This also is not capable of preventing overheating of the friction surfaces in all cases.